Rails: Asset not precompiled

Quick fix

Read the commands before running them. Anything that restarts a service, deletes data or changes permissions should be tried on a non-production system first.

# Precompile assets
RAILS_ENV=production bundle exec rails assets:precompile
# Add custom assets to precompile list in config/initializers/assets.rb
Rails.application.config.assets.precompile += %w( admin.js admin.css )
# Clear old assets
bundle exec rails assets:clobber

How to diagnose Ruby errors

Ruby errors are dominated by Bundler and gem resolution, native extension compilation (which needs system headers Ruby cannot install for you), and in Rails by the pending-migration and asset-precompilation guards. Those guards are deliberate safety checks, so the fix is to satisfy them rather than to disable them.

If the quick fix above does not resolve it, work through these steps. They apply to this whole class of error, not just to this one message, which is usually what saves the time.

1. Run bundle install with verbose output and read which gem fails and why. Native extension failures name the missing header in the mkmf log.
2. Check the mkmf log path the error prints. It contains the actual compiler error, which the Bundler summary truncates.
3. For Rails migration errors, run rails db:migrate:status to see exactly which migrations the database has recorded.
4. For asset errors in production, confirm rails assets:precompile ran during deployment and that the manifest is present in public/assets.
5. Verify the Ruby version matches .ruby-version and the Gemfile. Version managers silently switch, producing gem-not-found errors for gems that are installed elsewhere.

Tools worth reaching for

• bundle install --verbose
• rails db:migrate:status
• gem env
• rbenv/rvm version check
• bundle exec

Authoritative references

Primary documentation for this error, worth reading before applying any fix in production.

📖 guides.rubyonrails.org

Related Ruby errors

• Bundler: Could not find gemBundler cannot locate the specified gem in any of the configured sources (e.g., RubyGems).
• Encoding::InvalidByteSequenceErrorA string contains bytes that are invalid for the expected encoding (e.g., invalid UTF-8 bytes).
• LoadError: cannot load such fileRuby cannot find the required file or gem. The gem may not be installed, or the require path…
• Rails: ActionController::InvalidAuthenticityTokenThe CSRF token in the request did not match the one in the session. Rails keeps the session…
• Rails: No route matchesThe requested URL does not match any route defined in config/routes.rb.
• Rails: PendingMigrationErrorDatabase schema migrations have not been applied to the database.
• Ruby: can't modify frozen StringThe string is frozen, either by a `# frozen_string_literal: true` magic comment, by Ruby's…
• Ruby: Failed to build gem native extensionA gem with C extensions failed to compile because system libraries or development headers are…

See all 11 Ruby errors →

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This entry is maintained by hand. If the fix is out of date, incomplete, or you have a better one, email a correction and it will be reviewed.